Method and apparatus for measuring humidity using an electrochemical gas sensor

ABSTRACT

A gas detection apparatus and method for measuring humidity using an electrochemical gas sensor. The gas detection apparatus comprises an electrolyte-based electrochemical gas sensor and a controller configured to measure the average humidity value within an ambient environment over a period of time. The average ambient humidity value over the period of time is determined based on the average rate of change over the period of time of the electrolyte concentration within the electrolyte gas sensor of the gas detection apparatus over the period and the average temperature in the ambient environment over the period of time. The gas sensing apparatus may be configured to communicate the average ambient humidity value within the ambient environment to a second electrochemical gas sensor or a second gas detection apparatus within the same ambient environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.16/376,624, filed Apr. 5, 2019 and entitled “Method and Apparatus forMeasuring Humidity Using an Electrochemical Gas Sensor,” which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Various embodiments described herein relate generally to electrochemicalgas sensors. In particular, various embodiments are directed toelectrolyte-based gas sensors configured for measuring ambient humidity.

BACKGROUND

Industrial and commercial applications may use electrolyte-basedelectrochemical gas sensors to detect the presence of various gasses.The ambient humidity present within a conventional electrolyte-basedelectrochemical gas sensor's environment may cause a change in thesensor's electrolyte concentration due to water uptake or water losswith the ambient environment. The resulting change in electrolyteconcentration affects the performance of the sensor, often leading toinaccurate sensor measurement, decreased measurement sensitivity, andeven sensor failure. For this reason, some electrolyte-basedelectrochemical gas sensors incorporate conventional humidity sensors tomeasure ambient humidity and compensate for the resulting change inelectrolyte concentration in order to appropriately calibrate thesensor's output. Conventional humidity sensors, however, are oftenexpensive and bulky, thus increasing both the production costs and thefootprint associated with the collective sensory components. Further,existing humidity sensors used in this context often produce unreliablereadings and have relatively short lifespans—particularly when exposedto humidity extremes—compared to electrochemical gas sensors.

Accordingly, there is a need in the art for electrochemical gas sensorsequipped with a reliable, long-lasting solution for measuring humiditycharacterized by lower product costs and a minimized sensor footprint.

BRIEF SUMMARY

Various embodiments relate to methods and apparatuses for reliablymeasuring humidity using an electrolyte-based electrochemical gassensor.

Various embodiments are directed to a method for detecting gas using anelectrochemical gas sensor and a gas detection apparatus comprising afirst electrolyte-based electrochemical gas sensor configured to measurean electrolyte concentration within the first electrochemical gassensor; a temperature sensor configured to measure a temperature of anambient environment surrounding the first electrolyte-basedelectrochemical gas sensor; and a controller in communication with thefirst electrolyte-based electrochemical gas sensor and the temperaturesensor, wherein the controller may be configured to (i) determine anaverage ambient temperature of the ambient environment over a firstperiod of time, (ii) determine an average rate of change of electrolyteconcentration within the first electrochemical gas sensor over the firstperiod of time, and (iii) determine, based on the average ambienttemperature and the average rate of change of electrolyte concentration,an average humidity value of the ambient environment over the firstperiod of time.

In various embodiments, the first electrochemical gas sensor maycomprise a volume of acid-based electrolyte. Further, in variousembodiments, the controller of the gas detection apparatus may beconfigured to determine an average electrolyte vapor pressure over aperiod of time. In various embodiments, the temperature sensor may beintegrated into the first electrochemical gas sensor. In variousembodiments, a gas detection apparatus housing, wherein the gasdetection apparatus housing may comprise an exterior housing portion andan interior housing portion, and wherein the first electrochemical gassensor, the temperature sensor, and the controller may be enclosedwithin the interior housing portion.

In various embodiments, the average humidity value of the ambientenvironment over the first period of time may be determined using alook-up table correlating the average rate of change of electrolyteconcentration within the first electrochemical gas sensor over the firstperiod of time to a corresponding humidity value at the average ambienttemperature and an average electrolyte vapor pressure within the firstelectrochemical gas sensor over the first period of time. Further, invarious embodiments, the corresponding humidity value may define theaverage humidity value of an ambient environment over the first periodof time.

In various embodiments, a gas detection apparatus may further comprise asecond electrochemical gas sensor, wherein the second electrochemicalgas sensor may be an electrolyte-based electrochemical gas sensorpositioned within the ambient environment, and wherein the firstelectrochemical gas sensor may be configured to communicate the averagehumidity value of the ambient environment over the first period of timeto the second electrochemical gas sensor. In various embodiments, thesecond electrochemical gas sensor may comprise a volume ofnon-acid-based electrolyte. Further in various embodiments, the secondelectrochemical gas sensor may be configured to apply an appropriatecompensation factor to an output of the second electrochemical gassensor based on the average humidity value of the ambient environmentover the first period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 illustrates an exploded view of a gas sensor according to oneembodiment.

FIG. 2 schematically illustrates a cross-section drawing of anelectrochemical sensor according to one embodiment.

FIG. 3 illustrates a graph of current vs. potential according to oneembodiment.

FIG. 4A illustrates a graph of potential difference vs. anodic swingaccording to one embodiment.

FIG. 4B illustrates a graph of potential difference vs. anodic swing,corrected for anodic swing, according to one embodiment.

FIG. 4C illustrates a graph of potential difference vs. concentration ofthe electrolyte according to one embodiment.

FIG. 5 illustrates an example schematic block diagram in accordance withsome example embodiments described herein.

FIG. 6 illustrates data flows among components in accordance with someembodiments discussed herein.

FIG. 7 illustrates a flow diagram of an exemplary method of measuringhumidity using an electrochemical gas sensor in accordance with someexample embodiments described herein.

FIG. 8 illustrates an exemplary graphical representation of dataproduced by a testing configuration in accordance with variousembodiments.

FIG. 9 illustrates an exemplary graphical representation of dataproduced by a testing configuration in accordance with variousembodiments.

FIG. 10 illustrates an exemplary graphical representation of dataproduced by a testing configuration in accordance with variousembodiments.

DETAILED DESCRIPTION

The following description should be read with reference to the drawingswherein like reference numerals indicate like elements throughout theseveral views. The detailed description and drawings show severalembodiments which are meant to be illustrative of the disclosure. Itshould be understood that any numbering of disclosed features (e.g.,first, second, etc.) and/or directional terms used in conjunction withdisclosed features (e.g., front, back, top, bottom, side, and the like)are relative terms indicating illustrative relationships between thepertinent features.

It should be understood at the outset that although illustrativeimplementations of one or more aspects are illustrated below, thedisclosed assemblies, systems, and methods may be implemented using anynumber of techniques, whether currently known or not yet in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, but may bemodified within the scope of the appended claims along with their fullscope of equivalents. While values for dimensions of various elementsare disclosed, the drawings may not be to scale.

The words “example,” or “exemplary,” when used herein, are intended tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as an “example” or “exemplaryembodiment” is not necessarily preferred or advantageous over otherimplementations.

Overview

Described herein is a method and apparatus for reliably measuringhumidity using an electrolyte-based electrochemical gas sensor.Electrochemical gas sensors that operate based on aqueous electrolytes(e.g., acid-based electrolytes) may exhibit changes in electrolyteconcentration due to water uptake or water loss with the ambientenvironment. In particular, the concentration of aqueous electrolyte inelectrolyte-based electrochemical gas sensors may vary in response tothe ambient humidity. Accordingly, it may be desirable to characterizethe average humidity of a sensor's ambient environment over a period oftime in order to characterize that sensor's change in electrolyteconcentration. The method and apparatus disclosed herein provides asolution for determining the average humidity value for an ambientenvironment over a period of time using a measured change in theelectrolyte concentration of an electrochemical gas sensor and themeasured average ambient temperature over that period of time.

As described herein, the method and apparatus disclosed mayadvantageously measure humidity based in part on a rate of change inelectrolyte concentration within an electrochemical gas sensor. Thedisclosed methods and apparatuses therefore eliminate the need forseparate humidity sensors in order to appropriately compensate thereadings of such sensors based on ambient relative humidity.Additionally, the disclosed methods and apparatuses enable themeasurement of relative humidity with an increased degree of reliabilityand may result in an increased sensor lifespan. Further, by determininghumidity using existing hardware of an electrochemical gas sensor, themethod and apparatus described herein will minimize the sensor'sfootprint and ultimately save production costs.

In one exemplary embodiment, a method for determining humidity using anelectrochemical gas sensor may further comprise using the determinedaverage humidity value over a period of time in order to determine thechange in electrolyte concentration for those types of electrochemicalgas sensor in which the electrolyte concentration may be difficult todetermine (e.g., those that do not utilize an acid-based electrolyte).For example, it can be difficult, if not impossible, to measure changesin electrolyte concentration for electrolyte-based electrochemical gassensors utilizing non-acid-based electrolytes (e.g., salt-basedelectrolytes, ionic liquid-type electrolytes, organic electrolytes).According to various embodiments, average humidity values determinedfrom acid-based electrochemical gas sensors are therefore used tocompensate for the measurements of non-acid based electrochemical gassensors. In such embodiments, the overall accuracy of a system utilizingboth acid-based and non-acid-based sensors can therefore be improved.

Apparatus

In various embodiments, as disclosed herein a gas detection apparatus100 may comprise an electrochemical gas sensor and a controllerconfigured to determine the average humidity over a period of time bymeasuring the electrolyte concentration within the electrochemical gassensor and the temperature of the gas sensor's ambient environment overthe given period of time.

FIG. 1 illustrates an exploded view of an exemplary electrochemicalsensor 10 that may be used in accordance with the various embodiments ofthe apparatus and method described herein. Micro-electrodes 12, 14 areinstalled in sensor 10 at the positions shown at separator 12-1 near aworking electrode 20 (which may also be known as a sensing electrode),and at separator 14-1 between the reference and counter electrodes 22,24.

Electrolyte E is contained in the housing 26. Micro-electrodes 12, 14are immersed in the electrolyte E, and are not in the direct path of thetarget gas.

The above described electrodes such as 12, 14, 20, 22, and 24 along withthe electrolyte E are carried in a housing 26. Housing 26 can include avent 30 as would be understood by those of skill in the art. Sensor 10can be carried by a gas detector 10 a, in an external housing 10 b.

Electrical connecting elements, indicated at 26-1, carried by housing 26are coupled to the various electrodes in the housing 26. A power supply26-2, which could be implemented as a rechargeable battery, could becarried in external housing 10 b to energize the gas detector 10 a.

External housing 10 b can also carry control circuits 10 c which arecoupled to the connector elements 26-1 to receive signals from andcoupled signals to the electrodes 20, 22, 24 so as to sense conditionsin the sensor 10, or to control the operation of one or more electrodes20, 22, 24 to carry out the operational and diagnostic methods describedherein.

The gas detector 10 a can communicate via interface circuits 10 d,coupled to control circuits 10 c, via a medium M (which could be wired,or wireless), with displaced monitoring systems. The control circuits 10c can be implemented, at least in part, with a programmable processor 10e which executes pre-stored control instructions 10 f. In variousembodiments, the processor may be configured to receive sensory readingsmeasuring, for example, temperature, pressure, and electrolyteconcentration.

Exemplary micro-electrodes can be fabricated from PTFE coated platinumwire (Advent research materials part number PT5431, comprising 75 μηιdiameter platinum wire with approximately 18 μηι thick PTFE coating). Insome embodiments, the micro-electrodes 12, 14 may comprise a 50 μηιdiameter platinum wire that is approximately 6 mm long and immersed inthe electrolyte E. The wire can be cut with a scalpel to produce amicrodisc electrode inside the sensor 10, and the PTFE insulationstripped from the end of the wire external to the sensor 10 to allowelectrical contact to be made. The exposed tip of the wire can be pushedinto the respective separators 12-1, 14-1 to avoid it shorting againstthe adjacent electrodes 20, 22 24. However an alternative approachincludes sandwiching the micro-electrodes 12, 14 between two separators.Other configurations come within the spirit and scope of the invention.For example, the micro-electrodes may comprise uninsulated platinum wireand may operate as micro-cylinder electrodes, or they may be formed bydeposition of platinum onto a contact pin or pad by techniques such aselectroplating or sputtering, or by thick film printing platinum onto aceramic substrate. In some embodiments, each micro-electrode 12, 14 maybe used for separate diagnostic purposes, such as hydrogen peakreference, oxygen peak identification, etc. In various embodiments, anexemplary micro-electrode may be fabricated by welding a piece ofplatinum wire that may comprise, for example, a diameter between 25 umand 75 um (e.g., 50 um) and a substantially small length (e.g., 1 mm) toan end of an electrochemically inert supporting wire comprised of asuitable material (e.g., tantalum).

In some embodiments, scanning voltammetry may be completed on one ormore of the micro-electrodes 12, 14 to provide one or more diagnosticscans. Scanning voltammetry is an electrochemical technique whichmeasures the current that develops in an electrochemical cell underconditions where voltage is in excess of that predicted by the Nernstequation. Voltammetry is performed by cycling the potential of anelectrode, and measuring the resulting current. In scanning voltammetry,the electrode potential may ramp linearly versus time in cyclicalphases. In some embodiments, other waveforms may be used to complete thescanning voltammetry. For example, the waveform may be a steppedstaircase (staircase voltammetry) or a staircase with additionalsuperimposed positive and negative steps (square wave voltammetry). Therate of voltage change over time during each of these phases is known asthe experiment's scan rate (V/s). The results of a scanning voltammetryscan on one or more of the micro-electrodes 12, 14 may generatediagnostic information about the sensor 10.

FIG. 2 illustrates a cross-section drawing of an electrochemical sensor210. The sensor 210 generally comprises a housing 212 defining a cavityor reservoir 214 designed to hold an electrolyte solution. A workingelectrode 224 can be placed between an opening 228 and the reservoir214. A counter electrode 216 and a reference electrode 220 can bepositioned within the reservoir 214. When the gas reacts at theinterface between the working electrode 224 and the electrolyte withinthe separator 222, an electrical current and/or potential can bedeveloped between the electrodes 216, 220 to provide an indication ofthe concentration of the gas. A reference electrode 220 may also bepositioned within the reservoir 214 to provide a reference for thepotential at the working electrode.

The housing 212 defines the interior reservoir 214, and one or moreopenings 228 can be disposed in the housing 212 to allow a gas to bedetected to enter the housing 212 into a gas space 226. The housing 212can generally be formed from any material that is substantially inert tothe electrolyte and gas being measured. In an embodiment, the housing212 can be formed from a polymeric material, a metal, or a ceramic. Forexample, the housing can be formed from a material including, but notlimited to, acrylonitrile butadiene styrene (ABS), polyphenylene oxide(PPO), polystyrene (PS), polypropylene (PP), polyethylene (PE) (e.g.,high density polyethylene (HDPE)), polyphenylene ether (PPE), or anycombination or blend thereof. [0038] One or more openings 228 can beformed through the housing 212 to allow the ambient gas to enter the gasspace 226 and/or allow any gases generated within the housing 212 toescape. In an embodiment, the electrochemical sensor 210 may comprise atleast one inlet opening 228 to allow the ambient gas to enter thehousing 212. The opening 228 can be disposed in a cap when a cap ispresent and/or in a wall of the housing 212. In some embodiments, theopening 228 can comprise a diffusion barrier to restrict the flow of gas(e.g., carbon monoxide, hydrogen sulfide, oxygen, etc.) to the workingelectrode 224. The diffusion barrier can be created by forming theopening 228 as a capillary, and/or a film or membrane can be used tocontrol the mass flow rate through the one or more openings 228.

In an embodiment, the opening 228 may serve as a capillary opening toprovide a rate limited exchange of the gases between the interior andexterior of the housing 212. In an embodiment, the opening 228 may havea diameter between about 200 μηι and about 1.5 mm, where the opening 228can be formed using a conventional drill for larger openings and a laserdrill for smaller openings. The opening 228 may have a length betweenabout 0.5 mm and about 5 mm, depending on the thickness of the cap orhousing 212. In some embodiments, two or more openings may be presentfor the inlet gases. When a membrane is used to control the gas flowinto and/or out of the housing, the opening diameter may be larger thanthe sizes listed above as the film can contribute to and/or may beresponsible for controlling the flow rate of the gases into and out ofthe housing 212.

The reservoir 214 comprises the counter electrode 216, the referenceelectrode 220, and the working electrode 224. In some embodiments, theelectrolyte can be contained within the reservoir 214, and the counterelectrode 216, the reference electrode 220, and the working electrode224 can be in electrical contact through the electrolyte. In someembodiments, one or more porous separators 218, 222 or other porousstructures can be used to retain the electrolyte in contact with theelectrodes 216, 220, 224. The separators 218, 222 can comprise a porousmember that acts as a wick for the retention and transport of theelectrolyte between the reservoir 214 and the electrodes 216, 220, 224while being electrically insulating to prevent shorting due to directcontact between any two electrodes. One or more of the porous separators218, 222 can extend into the reservoir 214 to provide the electrolyte apath to the electrodes 216, 220, 224. In an embodiment, a separator 218can be disposed between the counter electrode 216 and the referenceelectrode 220, and a separator 222 can be disposed between the referenceelectrode 220 and the working electrode 224.

One or more of the separators 218, 222 can comprise a nonwoven porousmaterial (e.g., a porous felt member), a woven porous material, a porouspolymer (e.g., an open cell foam, a solid porous plastic, etc.), or thelike, and is generally chemically inert with respect to the electrolyteand the materials forming the electrodes. In an embodiment, theseparators 218, 222 can be formed from various materials that aresubstantially chemically inert to the electrolyte including, but notlimited to, glass (e.g., a glass mat), polymer (plastic discs),ceramics, or the like.

The electrolyte can be any conventional aqueous acidic electrolyte suchas sulfuric acid, phosphoric acid, or a neutral ionic solution such as asalt solution (e.g., a lithium salt such as lithium chloride, etc.), orany combination thereof. For example, the electrolyte can comprisesulfuric acid having a molar concentration between about 3 M to about 12M. Since sulfuric acid is hygroscopic, the concentration can vary fromabout 10 to about 70 wt % (1 to 11.5 molar) over a relative humidity(RH) range of the environment of about 3 to about 95%. In an embodiment,the electrolyte can comprise phosphoric acid having a concentration inan aqueous solution between about 30% to about 60% H3PO4 by weight. Asanother example, the electrolyte can include a lithium chloride salthaving about 30% to about 60% LiCl by weight, with the balance being anaqueous solution. As another example, a proton conducting ionic liquidmay be used.

In some embodiments, the electrolyte may be in the form of a solidpolymer electrolyte which comprises an ionic exchange membrane. In someembodiments, the electrolyte can be in the form of a free liquid,disposed in a matrix or slurry such as glass fibers (e.g., the separator218, the separator 222, etc.), or disposed in the form of a semi-solidor solid gel.

The working electrode 224 may be disposed within the housing 212. Thegas entering the sensor 210 can contact one side of the workingelectrode 224 and pass through working electrode 224 to reach theinterface between the working electrode 224 and the electrolyte. The gascan then react to generate the current indicative of the gasconcentration. As disclosed herein, the working electrode 224 cancomprise a plurality of layers. The base or substrate layer can comprisea hydrophobic material or a hydrophobically treated material. Acatalytic material can be formed as an electrode on one side of theworking electrode 224 and placed in contact with the electrolyte.

In an embodiment, the working electrode 224 can comprise a poroussubstrate or membrane as the base layer. The substrate can be porous tothe gas of interest, which in some embodiments can comprise hydrogensulfide, carbon monoxide, or oxygen. In an embodiment, the substrate cancomprise a carbon paper formed of carbon or graphite fibers. In someembodiments, the substrate can be made to be electrically conductivethrough the addition of a conductive material such as carbon. The use ofcarbon may provide a sufficient degree of electrical conductivity toallow the current generated by the reaction of the gas with theelectrolyte at the surface of the working electrode 224 to be detectedby a lead coupled to the working electrode 224. Other electricallyconductive substrates may also be used such as carbon felts, porouscarbon boards, and/or electrically conductive polymers such aspolyacetylene, each of which may be made hydrophobic as described below.Alternatively, an electrically conductive lead can be coupled to thecatalytic layer to electrically couple the catalytic material to theexternal circuitry, as described in more detail herein. In anembodiment, the substrate can be between about 5 mils to about 20 milsthick in some embodiments.

The porous substrate can be hydrophobic to prevent the electrolyte frompassing through the working electrode 224. The substrate can be formedfrom a hydrophobic material, or the substrate can be treated with ahydrophobic material. In an embodiment, the substrate can be madehydrophobic through the impregnation of the substrate with a hydrophobicmaterial such as a fluorinated polymer (e.g., PTFE, etc.). In someembodiments, the substrate or membrane can comprise GEFC-IES (e.g., thecopolymer of perfluorosulfonic acid and PTFE, which is commerciallyavailable from Golden Energy Fuel Cell Co., Ltd.), Nafion® (a copolymerof polytetrafluoroethylene andperfluoro-3,6-dioxa-4-methyl-7-octene-sulfonic acid, which iscommercially available from Dupont™), or pure or nearly purepolytetrafluoroethylene (PTFE). The impregnation process can includedisposing a hydrophobic material containing solution or slurry on thesubstrate using a dipping, coating, or rolling process. Alternatively, adry composition such as a powder can be applied to the substrate. Insome embodiments, an optional sintering process can be used to infusethe hydrophobic material into the substrate to create the hydrophobicbase layer for the working electrode 224, where both sides of thehydrophobic base layer are hydrophobic. The sintering process can causethe hydrophobic polymer to bond or fuse with the carbon of the substrateto securely bond the hydrophobic material to the substrate.

The resulting substrates can contain about 30% to about 50% by weight ofthe hydrophobic polymer. The amount of hydrophobic material added to thesubstrate can affect the electrical conductivity of the substrate, wherethe electrical conductivity tends to decrease with an increased amountof the hydrophobic material. The amount of the hydrophobic polymer usedwith the substrate may depend on the degree of hydrophobicity desired,the porosity to the target gas, and the resulting electricalconductivity of the working electrode.

The catalytic layer can be formed by mixing the desired catalyst with abinder and depositing the mixture on the substrate material. The bindercan comprise a solution of perfluorinated ion electrolyte solution(e.g., GEFC-IES, Nafion®, etc.), a hydrophobic material such as PTFE,mixtures thereof, or the like. When used as a binder, the GEFC-IESNafion® and/or PTFE can affect the gas diffusion parameters whilesupporting the electrocatalyst and maximizing the interfaces betweencatalyst, gas, and electrolyte at which the electrochemical processesoccur. Glycol or other similar chemicals can be used as a diluent toform a catalyst slurry, recipe, or catalyst system, which can be printedon a substrate by a printer.

The catalytic layer might be deposited onto the substrate by, forexample, screen printing, filtering in selected areas from a suspensionplaced onto the substrate, by spray coating, or any other methodsuitable for producing a patterned deposition of solid material.Deposition might be of a single material or of more than one materialsequentially in layers, so as, for example, to vary the properties ofthe electrode material through its thickness or to add a second layer ofincreased electrical conductivity above or below the layer which is themain site of gas reaction. Once deposited, the printed element can besintered at an elevated temperature to form the electrode.

In the working electrode 224, the catalytic layer can comprise carbon(e.g., graphite) and/or one or more metals or metal oxides such ascopper, silver, gold, nickel, palladium, platinum, ruthenium, iridium,and/or oxides of these metals. The catalyst used can be a pure metalpowder, a metal powder combined with carbon, or a metal powder supportedon an electrically conductive medium such as carbon, or a combination oftwo or more metal powders either as a blend or as an alloy. Thematerials used for the individual electrodes can be the same ordifferent. In an embodiment, the working electrode 224 comprises aplatinum-ruthenium black (Pt—Ru black) electrode. The atomic ratio ofthe Pt to Ru in the Pt—Ru black electrode can be in the range of about1:1 to about 1:5, or about 1:2. The catalyst material can have a weightloading per square centimeter (cm<2>) of the surface area of the workingelectrode 224 of between about 0.1 mg/cm<2> and about 5 mg/cm<2>, orbetween about 0.5 mg/cm<2> and about 2 mg/cm<2>, or about 1 mg/cm<2>.

The counter electrode 216 can be disposed within the housing 212. Thecounter electrode 216 can comprise a substrate or membrane such as aPTFE membrane, a GEFC-IES membrane, a Nation® membrane, or the likehaving a catalytic material disposed thereon. In an embodiment, thecatalytic material can be mixed and disposed on the membrane using anysuitable process such as rolling, coating, screen printing, or the liketo apply the catalytic material on the membrane, as described in moredetail herein. The catalyst layer can then be bonded to the membranethrough a sintering process as described herein.

In an embodiment, the catalytic material for the counter electrode cancomprise a noble metal such as gold (Au), platinum (Pt), ruthenium (Ru),rhodium (Rh), Iridium (Ir), oxides thereof, or any combination thereof.In an embodiment, the catalytic material comprises a Pt—Ru mixture thatis screen printed on the membrane, where the membrane can be a GEFC-IESmembrane. The catalyst loading for the counter electrode 216 can bewithin any of the ranges described herein for the working electrode 224.In an embodiment, the catalyst loading for the counter electrode 216 canbe the same or substantially the same as the catalyst loading for theworking electrode 224, the catalyst loading can also be greater than orless than that of the working electrode 224. [0053] Similarly, thereference electrode 220 can be disposed within the housing 212. Thereference electrode 220 can comprise a substrate or membrane such as aPTFE membrane, a GEFC-IES membrane, a Nafion® membrane, or the likehaving a catalytic material disposed thereon. In an embodiment, thecatalytic material can be mixed with a hydrophobic material (e.g., PTFE,etc.) and disposed on the PTFE membrane. Any of the methods used to formthe working electrode or the counter electrode can also be used toprepare the reference electrode 220. In an embodiment, the catalyticmaterial used with the reference electrode 220 can comprise a noblemetal such as gold (Au), platinum (Pt), ruthenium (Ru), rhodium (Rh),Iridium (Ir), oxides thereof, or any combination thereof. In anembodiment, the catalytic material used to form the reference electrode220 can comprise a Pt—Ru mixture that is screen printed on the membrane,where the membrane can be a GEFC-IES membrane. The catalyst loading forthe reference electrode 220 can be within any of the ranges describedherein for the working electrode 224. In an embodiment, the catalystloading for the reference electrode 220 can be the same or substantiallythe same as the catalyst loading for the working electrode 224, thecatalyst loading can also be greater than or less than that of theworking electrode 224. While illustrated in FIG. 1 as having thereference electrode 220, some embodiments of the electrochemical sensormay not include a reference electrode 220.

In order to detect the current and/or potential difference across theelectrodes in response to the presence of the target gas, one or moreleads or electrical contacts can be electrically coupled to the workingelectrode 224, the reference electrode 220, and/or the counter electrode216. The lead contacting the working electrode 224 can contact eitherside of the working electrode 224 since the substrate comprises anelectrically conductive material. In order to avoid the corrosiveeffects of the electrolyte, the lead contacting the working electrode224 can contact the side of the working electrode 224 that is not incontact with the electrolyte. Leads may be similarly electricallycoupled to the counter electrode 216 and the reference electrode 220.The leads can be electrically coupled to external connection pins toprovide an electrical connection to external processing circuitry. Theexternal circuitry can detect the current and/or potential differencebetween the electrodes and convert the current into a correspondingtarget gas concentration.

In some embodiments, the sensor 210 may comprise one or more diagnosticmicro-electrodes 232 and 234 (which may be similar to themicro-electrodes 12, 14 of FIG. 1). The diagnostic electrode may be awire (as shown in FIG. 2), where the exposed tip of the wire can bepushed into the separators 222, 218 to avoid it shorting against theadjacent electrodes. However an alternative approach includessandwiching the micro-electrodes 232, 234 between two separators. Otherconfigurations come within the spirit and scope of the invention. Forexample, the micro-electrodes may comprise uninsulated platinum wire andmay operate as micro-cylinder electrodes, or they may be formed bydeposition of platinum onto a contact pin or pad by techniques such aselectroplating or sputtering, or by thick film printing platinum onto aceramic substrate. In some embodiments, each micro-electrode 232, 234may be used for separate diagnostic purposes, such as hydrogen peakreference, oxygen peak identification, etc. The micro-electrodes maycomprise platinum, gold, ruthenium, rhodium, iridium, palladium,rhenium, osmium, or their alloys with each other or with other metals(e.g. platinum/nickel alloys).

In use, the sensor 210 can detect a target gas concentration. In use,the ambient gas can flow into the sensor 210 through the opening 228,which serves as the intake port for the sensor 210. The ambient gas cancomprise a concentration of the target gas, which may include hydrogensulfide, oxygen, and/or carbon monoxide. The gas can contact the workingelectrode 224 and pass through the fine pores of the porous substratelayer to reach the surface of the working electrode 224 treated with thecatalyst layer. The electrolyte may be in contact with the surface ofthe working electrode 224, and the target gas may react and result in anelectrolytic current forming between the working electrode 224 and thecounter electrode 216 that corresponds to the concentration of thetarget gas in the ambient gas. By measuring the current, theconcentration of target gas can be determined using, for example, theexternal detection circuitry.

In some embodiments of the disclosure, one or more elements of thesensor (as described above in FIGS. 1 and 2) may be scanned usingscanning voltammetry to observe the effects of changing concentration inthe electrolyte (E above).

An electrochemical sensor may be scanned using one or more of theelectrodes. In some embodiments, the scanning may be done on amicro-electrode within the sensor. The scan may generate a graph thatcontains a plurality of peaks due to adsorption, desorption, formation,and/or reduction of certain elements. The scanning may be completed at aplurality of electrolyte concentrations, wherein the graphs for each ofthe concentrations may be compared. In some embodiments, the graph mayshow one or more peaks that are consistent for each concentration, whichmay be considered reference peaks. Additionally, the graph may show oneor more peaks that change with concentration. The difference in voltagebetween the concentration dependent peak(s) and the reference peak(s)may provide a correlation for electrolyte concentration. Thiscorrelation may approximately linear when the axes of the graph areelectrolyte concentration and voltage difference between the two peaks.

Once a correlation is established, the electrolyte concentration forsimilar electrochemical sensors may be determined by completing avoltammetry scan on the sensor, and then identifying the relevant peaksto the correlation. Once the voltage difference between the peaks isidentified, the electrolyte concentration may be determined. Thedetermined electrolyte concentration may be used to correct sensorreadings, and/or to identify any other errors with the sensor.

In some embodiments, a diagnostic micro-electrode may be used tocomplete the voltammetry scans. The benefits to using a micro-electrodemay be that it would be lower power, require a shorter measurement time,suffers less distortion of the measurement due to ohmic losses in theelectrolyte, and it avoids disturbing the main gas working electrode.

The disclosure having been generally described, the following examplesare given as particular embodiments of the disclosure and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification or the claims in any manner.

FIG. 3 illustrates a staircase voltammogram of an exemplary electrode.To investigate the effects of the changing concentration of electrolytein the sensor cells, scanning voltammetry may be performed in a range ofH2SO4 solutions (0.6 M, 2.5 M, 5 M, 8 M, 10 M, and 12 M) and the resultsare shown in FIG. 3. In other words, using the same electrode, acidconcentration was varied between 0.6 M and 12 M.

The staircase voltammogram shown in FIG. 3 illustrates a plot generatedfrom an exemplary micro-electrode that comprises a 50 μηι diameterplatinum wire approximately 6 mm long immersed in electrolyte. Thescanning was completed at 5 V/s, with 2 mV steps, and 100% chargeintegration. The sensor was galvanostatically scanned 10 times betweenhydrogen (H2) and oxygen (O2) evolution to clean the electrode prior tovoltammetry scanning. The wire micro-electrode was driven relative tousual platinum reference and counter electrodes.

As shown in FIG. 3, hydrogen peaks (B, C, E, and F) occur at awell-defined potential and therefore can be used as a standardreference, where peak (C) is the most well-defined. The peaks indicatingoxide formation (G) and reduction (A) appear to be electrolyteconcentration dependent, where peak (G) is not always well defined.However peak (A) is always clear and easy to detect but its positionvaries with anodic swing (H). Therefore, to determine a correlation, theanodic swing (H) may be fixed relative to the hydrogen peak (C) so thatthe voltage difference (i.e. V(A)−V(C)) is then a measure of electrolyteconcentration. In the testing illustrated by FIG. 3, it was shown thatthe presence of oxygen does not interfere with the measurement.

FIG. 4A illustrates the oxide reduction peak position dependent on theanodic limit. The linear correlations are illustrated on the graph. Tocorrect for the anodic limit, the slopes of the linear correlations maybe adjusted. As shown in FIG. 4B a slope of approximately 0.2*x wasapplied to the data. FIG. 4B illustrates the correction for effects ofthe anodic limit. In another embodiment, the effect of the anodic limitmay be accounted for when determining the peak difference, whereinanodic limit may be defined relative to the hydrogen reference peak.

FIG. 4C illustrates the corrected peak difference values as a functionof electrolyte concentration. FIG. 4C shows that there is a strongcorrelation between the potential difference between the two peaks(oxide reduction and adsorbed hydrogen) and the concentration of theelectrolyte. Therefore, this measurement could therefore be used as anindicator of the concentration of the electrolyte. Additionally, thepotential appears to be linearly dependent on electrolyte concentrationover the full range of environmental interest (0.6 M-12 M).

In some embodiments, temperature may have an effect on the electrolyteconcentration measurement by diagnostic micro-electrode. The effect maybe small and may be easily compensated for by using a low accuracytemperature sensor. As an example, the observed peak separationincreased by around 1 mV/C, which may be equivalent to approximately0.07 M/C.

In some embodiments, the voltammetry may be completed using square wavevoltammetry (SWV). Using SWV may improve the definition of the hydrogenpeaks over traditional staircase voltammetry. In some embodiments, bothtechniques may be used. For example, SWV may be used to determine thehydrogen peaks, and then subsequent staircase voltammetry may be used todetermine the oxide reduction peak. Also, square wave voltammetry allowsfor detection of an additional peak for oxide formation (which isnormally only a shoulder in voltammetry). This additional peak is also afunction of both electrolyte concentration and temperature, so it couldbe used in addition to or instead of the oxide reduction peak. Onebenefit of using the above described method is that the position of theoxide formation peak (G) is not affected by the anodic limit since it isformed on the anodic scan, therefore it is not necessary to perform thecorrection shown in FIG. 4B or to control the anodic limit. A furtherbenefit of using the oxide formation peak (G) is that it gives ameasurement which is more sensitive to the electrolyte concentration andless sensitive to temperature. The following equations were obtained byfitting the results of square voltammetry on sensors of the design shownin FIG. 1, with a range of sulphuric acid concentrations from 7 to 14 Mover a temperature range from 20 C to 50 C.

V(A−C)=552+0.582×Temperature+10.44×Concentration

V(G−C)=852+0.102×Temperature+17.59×Concentration

Where V(A−C) is the potential difference in millivolts between the oxidereduction peak and a hydrogen peak, V(G−C) is the potential differencein millivolts between the oxide formation peak and a hydrogen peak,temperature is in degrees Celsius and Concentration is in moles perliter. The use of the formation peak gives a more sensitive measure ofthe electrolyte concentration with less need for temperaturecompensation. Alternatively, the two equations can be solvedsimultaneously to allow both the concentration and temperature to bedetermined, avoiding the need for a separate temperature sensor to bepresent.

Square wave voltammetry adds additional parameters which can be adjustedto optimize the measurement. For example, variation of step heightchanges the intensities of the oxide peaks but does not affect thehydrogen peaks. So SWV could be used to optimize the peaks for ease ofmeasurement or to help distinguish between the peak types, therebysimplifying the detection methods.

The example gas detection apparatus 100 described herein, such ascontroller 500 shown in FIG. 5. As illustrated in FIG. 5, the controller500 may comprise a temperature measurement circuitry 501, and pressuremeasurement circuitry 503, processing circuitry 508, a potentiostat 502,input/output circuitry 504, power circuitry 505, memory 506,communication circuitry 507, humidity measurement circuitry 510,electrolyte content monitoring circuitry 509, electrochemical gasmonitoring circuitry 511, and electrochemical gas detection circuitry512.

The use of the term “circuitry” as used herein with respect tocomponents of the gas detection apparatus 100 therefore includesparticular hardware configured to perform the functions associated withrespective circuitry described herein. Of course, while the term“circuitry” should be understood broadly to include hardware, in someembodiments, circuitry may also include software for configuring thehardware. For example, in some embodiments, “circuitry” may includeprocessing circuitry, storage media, network interfaces, input-outputdevices, and other components. In some embodiments, other elements ofthe controller 500 may provide or supplement the functionality ofparticular circuitry. For example, the processing circuitry 508 mayprovide processing functionality, memory 506 may provide storagefunctionality, and communication circuitry 507 may provide networkinterface functionality, among other features.

The temperature measurement circuitry 501 includes hardware componentsdesigned or configured to receive, process, generate, and transmit data,such as ambient temperature data. In various embodiments, thetemperature measurement circuitry 501 may be configured to measure thetemperature of the ambient environment within which the gas detectionapparatus 100 is located. In various embodiments, the temperaturemeasurement circuitry 501 may be configured to measure the ambienttemperature over one or more time intervals. Further, the temperaturemeasurement circuitry 501 may be configured to determine the change intemperature or the average temperature over the one or more timeintervals. In various embodiments, the temperature measurement circuitry501 may be positioned either within or outside of the electrochemicalgas sensor housing and may further be integrated into one or morecomponents of the gas detection apparatus 100 (e.g., the electrochemicalgas sensor).

The pressure measurement circuitry 503 includes hardware componentsdesigned or configured to receive, process, generate, and transmit data,such as electrolyte water vapor pressure data. In various embodiments,the pressure measurement circuitry 503 may be configured to determinethe vapor pressure of an electrolyte present within the electrochemicalgas sensor. In various embodiments, the electrolyte water vapor pressuremay be a function of one or more of the measured electrolyteconcentration values of the electrochemical gas sensor, the measuredambient temperature, and the total volume of water present within theelectrochemical gas sensor. In various embodiments, the pressuremeasurement circuitry 503 may be configured to determine the electrolytewater vapor pressure over one or more time intervals. Further, thepressure measurement circuitry 503 may be configured to determine thechange in electrolyte water vapor pressure or the average electrolytewater vapor pressure over the one or more time intervals. In variousembodiments, the pressure measurement circuitry 503 may be positionedeither within or outside of the electrochemical gas sensor housing andmay further be integrated into one or more components of the gasdetection apparatus 100 (e.g., the electrochemical gas sensor).

In some embodiments, the controller 500 may include input-outputcircuitry 504 that may, in turn, be in communication with the processingcircuitry 508 to provide output to the user and, in some embodiments, toreceive input such as a command provided by the user. As shown in FIG.6, the input-output circuitry 504 may comprise a user interface 190,such as a graphical user interface (GUI), and may include a display thatmay include a web user interface, a GUI application, a mobileapplication, a client device, or any other suitable hardware orsoftware. In some embodiments, the input-output circuitry 504 may alsoinclude a keyboard, a mouse, a joystick, a display device, a displayscreen, a touch screen, touch areas, soft keys, a microphone, a speaker(e.g., a buzzer), a light emitting device (e.g., a red light emittingdiode (LED), a green LED, a blue LED, a white LED, an infrared (IR) LED,an ultraviolet (UV) LED, or a combination thereof), or otherinput-output mechanisms. The processing circuitry 508, input-outputcircuitry 504 (which may utilize the processing circuitry), or both maybe configured to control one or more functions of one or more userinterface elements through computer-executable program code instructions(e.g., software, firmware) stored in a non-transitory computer-readablestorage medium (e.g., memory 506). Input-output circuitry 504 isoptional and, in some embodiments, the controller 500 may not includeinput-output circuitry. For example, where the controller 500 does notinteract directly with the user, the controller 500 may generate userinterface data for display by one or more other devices with which oneor more users directly interact and transmit the generated userinterface data to one or more of those devices. For example, thecontroller 500, using user interface circuitry may generate userinterface data for display by one or more display devices and transmitthe generated user interface data to those display devices

In various embodiments, the power circuitry 505 may be configured toreceive power and power gas detection apparatus 100. As non-limitingexamples, the power circuitry 505 may comprise one or more batteries,one or more capacitors, one or more constant power supplies (e.g., awall-outlet), and/or the like. In some embodiments, the power circuitry505 may comprise an external power supply positioned outside of theapparatus housing 110 and configured to deliver alternating or directcurrent power to the gas detection apparatus 100. Further, in someembodiments, as illustrated in FIG. 5, the power circuitry 505 maycomprise an internal power supply, for example, one or more batteries,positioned within the apparatus housing 110.

In some embodiments, the processing circuitry 508 (and/or co-processoror any other processing circuitry assisting or otherwise associated withthe processor) may be in communication with the memory 506 via a bus forpassing information among components of the apparatus. The memory 506may be non-transitory and may include, for example, one or more volatileand/or non-volatile memories. For example, the memory 506 may be anelectronic storage device (e.g., a computer readable storage medium). Inanother example, the memory 506 may be a non-transitorycomputer-readable storage medium storing computer-executable programcode instructions that, when executed by a computing system, cause thecomputing system to perform the various operations described herein. Thememory 506 may be configured to store information, data, content,signals applications, instructions (e.g., computer-executable programcode instructions), or the like, for enabling the controller 500 tocarry out various functions in accordance with example embodiments ofthe present disclosure. For example, the memory 506 may be configured tostore electrolyte content monitoring techniques; capacitance measurementtechniques; impedance measurement techniques; monitored data; ranges ofmonitored data; ranges of frequencies (e.g., band-gap filters);electrolyte content monitoring signals; temperature measurement signals,temperature measurement data, pressure measurement signals, pressuremeasurement data, water volume content data, humidity determinationtechniques, humidity measurement look-up tables, humidity measurementdata, any other suitable data or data structures; or any combination orcombinations thereof. It will be understood that the memory 506 may beconfigured to store partially or wholly any electronic information,data, data structures, embodiments, examples, figures, processes,operations, techniques, algorithms, instructions, systems, apparatuses,methods, or computer program products described herein, or anycombination thereof. In various embodiments, a look-up table may be adata matrix used to define a relationship between a rate of change ofelectrolyte concentration over a first period of time to a correspondinghumidity value at an ambient temperature and an electrolyte water vaporpressure. Further, a look-up table as described herein may correlate theaverage rate of change of electrolyte concentration within the firstelectrochemical gas sensor over the first period of time to acorresponding humidity value at the average ambient temperature and anaverage electrolyte water vapor pressure within the firstelectrochemical gas sensor over the first period of time, wherein thecorresponding humidity value defines the average humidity value of anambient environment over the first period of time.

The processing circuitry 508 may be embodied in a number of differentways and may, for example, include one or more processing devicesconfigured to perform independently. Additionally or alternatively, theprocessing circuitry 508 may include one or more processors configuredin tandem via a bus to enable independent execution of instructions,pipelining, multithreading, or a combination thereof. The use of theterm “processing circuitry” may be understood to include a single coreprocessor, a multi-core processor, multiple processors internal to theapparatus, remote or “cloud” processors, or a combination thereof.

In an example embodiment, the processing circuitry 508 may be configuredto execute instructions stored in the memory 506 or otherwise accessibleto the processing circuitry 508. Alternatively or additionally, theprocessing circuitry 508 may be configured to execute hard-codedfunctionality. As such, whether configured by hardware or softwaremethods, or by a combination of hardware with software, the processingcircuitry 508 may represent an entity (e.g., physically embodied incircuitry) capable of performing operations according to an embodimentof the present disclosure while configured accordingly. As anotherexample, when the processing circuitry 508 is embodied as an executor ofprogram code instructions, the instructions may specifically configurethe processor to perform the operations described herein when theinstructions are executed.

In various embodiments, the processing circuitry 508 may be furtherconfigured to control the potentiostat 502 to complete the voltammetryscans of the electrochemical gas sensor as described above.

The communication circuitry 507 may allow any of the sensory results orreadings communicated to the processing circuitry 508 as discussedherein (e.g., electrochemical gas monitoring circuitry 511 output,temperature measurement circuitry 501 output, pressure measurementcircuitry 503 output, humidity measurement circuitry 510 results) to befurther communicated to an external source. The communication circuitry507 may include, for example, a network interface for enablingcommunications with a wired or wireless communication network. Forexample, the communication circuitry 507 may include one or more networkinterface cards, antennae, buses, switches, routers, modems, andsupporting hardware and/or software, or any other device suitable forenabling communications via a network. In some embodiments, thecommunication interface may include the circuitry for interacting withthe antenna(s) to cause transmission of signals via the antenna(s) or tohandle receipt of signals received via the antenna(s). These signals maybe transmitted or received by the gas detection apparatus 100 using anyof a number of Internet, Ethernet, cellular, satellite, or wirelesstechnologies, such as IEEE 802.11, Code Division Multiple Access (CDMA),Global System for Mobiles (GSM), Universal Mobile TelecommunicationsSystem (UMTS), Long-Term Evolution (LTE), Bluetooth® v1.0 through v5.0,Bluetooth Low Energy (BLE), infrared wireless (e.g., IrDA),ultra-wideband (UWB), induction wireless transmission, Wi-Fi, near fieldcommunications (NFC), Worldwide Interoperability for Microwave Access(WiMAX), radio frequency (RF), RFID, or any other suitable technologies.

In various embodiments, the processing circuitry 508 may be configuredto communicate with the humidity measurement circuitry 510. The humiditymeasurement circuitry 510 may include hardware components designed orconfigured to receive, process, generate, and transmit data, such asambient humidity data. In various embodiments, the humidity measurementcircuitry 510 may be configured to determine the humidity of the ambientenvironment within which the gas detection apparatus 100 is located. Invarious embodiments, the ambient humidity may be a function of one ormore of the rate of change of electrolyte concentration within theelectrochemical gas sensor, the measured ambient temperature, and theelectrolyte water vapor pressure. In various embodiments, the humiditymeasurement circuitry 501 may be configured to determine the ambienthumidity over one or more time intervals. Further, the humiditymeasurement circuitry 510 may be configured to determine the averageambient humidity over the one or more time intervals. In variousembodiments, the humidity measurement circuitry 510 may be configured todetermine the average ambient humidity over a period of time byretrieving electrolyte concentration data defining the average rate ofchange of electrolyte concentration within the electrochemical gassensor over the period of time, and, based on data in a look-up tablestored in memory 504 that correlates a rate of change of electrolyteconcentration to a relative humidity value, determining the relativehumidity value corresponding to the average rate of change ofelectrolyte concentration—at an average ambient temperature determinedby the temperature measurement circuitry 501 and an average electrolytewater vapor pressure determined by the pressure measurement circuitry503—over the period of time. The humidity measurement circuitry 510 maybe configured to correlate the determined relative humidity value fromthe look-up table to the average ambient humidity over the period oftime. In various embodiments, the humidity measurement circuitry 501 maybe configured to communicate with one or more of the various componentsof the controller 500.

The user interface circuitry as described herein may include hardwarecomponents designed or configured to receive, process, generate, andtransmit data, such as user interface data. In some embodiments, theuser interface circuitry may be configured to generate user interfacedata indicative of a set of monitoring modes for a particular gas typeor environment, electrochemical gas monitoring signals, RMSelectrochemical gas monitoring signals, predetermined electrochemicalgas monitoring threshold value (e.g., settable by a user usinginput-output circuitry 504 or a user device in communication withinput-output circuitry 504; settable by accessing a table ofpredetermined electrochemical gas monitoring threshold values forvarious gas types), electrochemical gas alert signals, electrolytecontent monitoring signals, RMS electrolyte content monitoring signals,electrolyte content values (including, but not limited to, electrolytecontent percentage values), low electrolyte alert signals, pressurevalues, ambient temperature values, ambient humidity values, andcombinations thereof. In some instances, the user interface data maycomprise a list (e.g., a selectable drop-down list, a ordered groupingof selectable icons (e.g., clickable icons configured to be clicked by amouse; virtual icons configured to be displayed on a touchscreen andpressed by a user's finger), a text-based prompt, a voice-based prompt)of monitoring modes. For instance, the user interface circuitry mayinclude hardware components designed or configured to generate the userinterface data based on any embodiment or combination of embodimentsdescribed with reference to the figures included herein.

In some embodiments, the user interface circuitry may be incommunication with a display device (e.g., input-output circuitry 504, auser device, or a display device communicatively coupled thereto) andthus configured to transmit the user interface data to the displaydevice. For example, the user interface circuitry may be configured togenerate user interface data and transmit the generated user interfacedata to the input-output circuitry 504, and the input-output circuitry504 may be configured to receive the user interface data and display thereceived user interface data on one or more display screens.

In some embodiments, each of the electrochemical gas monitoringcircuitry 511, electrochemical gas detection circuitry 512, electrolytecontent monitoring circuitry 509, user interface circuitry, temperaturemeasurement circuitry 501, pressure measurement circuitry 503, andhumidity measurement circuitry 510 may include a separate processor,specially configured field programmable gate array (FPGA), applicationspecific interface circuit (ASIC), or cloud utility to perform the abovefunctions. In some embodiments, the hardware components described abovewith reference to the electrochemical gas monitoring circuitry 511,electrochemical gas detection circuitry 512, electrolyte contentmonitoring circuitry 509, user interface circuitry, temperaturemeasurement circuitry 501, pressure measurement circuitry 503, andhumidity measurement circuitry 510 may, for instance, utilizecommunications circuitry 507 or any suitable wired or wirelesscommunications path to communicate with a user device, each other, orany other suitable circuitry or device.

In some embodiments, one or more of the electrochemical gas monitoringcircuitry 511, electrochemical gas detection circuitry 512, electrolytecontent monitoring circuitry 509, user interface circuitry, temperaturemeasurement circuitry 501, pressure measurement circuitry 503, andhumidity measurement circuitry 510 may be hosted locally by thecontroller 500. In some embodiments, one or more of the user interfacecircuitry and the humidity measurement circuitry 510 may be hostedremotely (e.g., by one or more cloud servers) and thus need notphysically reside on the controller 500. Thus, some or all of thefunctionality described herein may be provided by a remote circuitry.For example, the controller 500 may access one or more remotecircuitries via any sort of networked connection that facilitatestransmission of data and electronic information between the controller500 and the remote circuitries. In turn, the controller 500 may be inremote communication with one or more of the electrochemical gasmonitoring circuitry 511, electrochemical gas detection circuitry 512,electrolyte content monitoring circuitry 509, user interface circuitry,temperature measurement circuitry 501, pressure measurement circuitry503, and humidity measurement circuitry 510.

As described above and as will be appreciated based on this disclosure,embodiments of the present disclosure may be configured as systems,apparatuses, methods, mobile devices, backend network devices, computerprogram products, other suitable devices, and combinations thereof.Accordingly, embodiments may comprise various means including entirelyof hardware or any combination of software with hardware. Furthermore,embodiments may take the form of a computer program product on at leastone non-transitory computer-readable storage medium havingcomputer-readable program instructions (e.g., computer software)embodied in the storage medium. Any suitable computer-readable storagemedium may be utilized including non-transitory hard disks, CD-ROMs,flash memory, optical storage devices, or magnetic storage devices. Aswill be appreciated, any computer program instructions and/or other typeof code described herein may be loaded onto a computer, processor orother programmable apparatus's circuitry to produce a machine, such thatthe computer, processor, or other programmable circuitry that executesthe code on the machine creates the means for implementing variousfunctions, including those described herein.

In some embodiments, the user device may be embodied by one or morecomputing devices or systems that also may include processing circuitry,memory, input-output circuitry, and communications circuitry. Forexample, a user device may be a laptop computer on which an app (e.g., aGUI application) is running or otherwise being executed by processingcircuitry. In yet another example, a user device may be a smartphone onwhich an app (e.g., a webpage browsing app) is running or otherwisebeing executed by processing circuitry. As it relates to operationsdescribed in the present disclosure, the functioning of these devicesmay utilize components similar to the similarly named componentsdescribed above with respect to FIG. 5. Additional description of themechanics of these components is omitted for the sake of brevity. Thesedevice elements, operating together, provide the respective computingsystems with the functionality necessary to facilitate the communicationof data with the example electrochemical gas sensor described herein.

As described above and as will be appreciated based on this disclosure,various embodiments may be configured in various forms including withportions of the gas detection apparatus 100 being remote from gasdetection apparatus 100 shown in FIG. 6. FIG. 6 illustrates exemplarydata flows among various components in accordance with a gas detectionapparatus 100 embodiment as discussed herein. In various embodiments,the communication circuitry 507 may be configured so as to enablewireless communication from the gas detection apparatus 100 within anInternet-of-Things (IoT) network 600 to a variety of wirelessly enableddevices (e.g., a user mobile device 601, a server 602, a computer 603, asecond gas detection apparatus 604). In an exemplary embodiment, the gasdetection apparatus 100 may be configured to communicate any of theaforementioned sensory results or readings communicated to theprocessing circuitry 508 (e.g., electrochemical gas monitoring circuitry511 output, temperature measurement circuitry 501 output, pressuremeasurement circuitry 503 output, humidity measurement circuitry 510results) to a second gas detection apparatus 604 configured for wirelesscommunication and present within substantially the same ambientenvironment. In various embodiments, the second gas detection apparatus604 may comprise one or more gas detection apparatuses as disclosedherein. In various embodiments, the second gas apparatuses 604 maycomprise an electrolyte-based electrochemical gas sensor for which theelectrolyte concentration may not be easily ascertained. For example,the second gas detection apparatus 604 may comprise an electrolyte-basedelectrochemical gas sensor utilizing a non-acid-based electrolyte, suchas a salt-based electrolyte, an ionic liquid-type electrolyte, or anorganic electrolyte. In various embodiments, the gas detection apparatus100 may communicate an average humidity value within an ambientenvironment as determined by the humidity measurement circuitry 510 ofthe gas detection apparatus 100 to the one or more secondary gasdetection apparatuses 604. In various embodiments, the one or moresecondary gas detection apparatuses 604 may be configured torespectively receive the average humidity value, thus enabling thecompensation of the apparatuses' respective sensor outputs.

Method of Use

FIG. 7 illustrates a block diagram of an exemplary method 700 formeasuring humidity using an electrochemical gas sensor.

The method 700 begins with step 701, in which electrolyte concentrationand average temperature a first measured. In particular, as shown instep 701A, the electrolyte concentration of an electrochemical gassensor within a gas detection apparatus is first measured. Methods formeasuring the electrolyte concentration of an electrochemical gas sensoras disclosed herein, or any other applicable means for determiningelectrolyte concentration of an electrochemical gas sensor may beimplemented. In various embodiments, the time at which the electrolyteconcentration of the electrochemical gas sensor is measured may definethe end of a first time interval.

As shown in step 701B, the average temperature of an ambient environmentwithin which the exemplary gas detection apparatus is located ismeasured over a first period of time. In various embodiments, theaverage ambient temperature over a first period of time may be measuredusing either an electrochemical gas sensor or a temperature sensor, andcorresponding temperature measurement circuitry (e.g., temperaturemeasurement circuitry 501).

Next, at step 702, a value associated with the electrolyte concentrationof the electrochemical gas sensor is stored at the beginning of thefirst period of time in a memory module (e.g., memory 504). In variousembodiments, the stored electrolyte concentration value may comprise avalue associated with the electrolyte concentration of theelectrochemical gas sensor at the end of a period of time immediatelypreceding the first period of time.

Next, at step 703, the average electrolyte water vapor pressure of anelectrochemical gas sensor over the first period of time is determined.In various embodiments, the electrolyte water vapor pressure may be afunction of one or more of the measured electrolyte concentration valuesof the electrochemical gas sensor and the measured ambient temperature.In various embodiments, the average electrolyte water vapor pressureover a period of time may be a function of the measured electrolyteconcentration value measured by the electrochemical gas sensor at theend of the first period of time (i.e. the value measured at step 701A),the stored value associated with the electrolyte concentration of anelectrochemical gas sensor at the beginning of the first period of time,and the measured average ambient temperature over the first period oftime. In various embodiments, the average electrolyte water vaporpressure in the electrochemical gas sensor over the first time periodmay be determined using pressure measurement circuitry (e.g., pressuremeasurement circuitry 503).

Next, at step 704, an average rate of change of electrolyteconcentration within an electrochemical gas sensor over the first periodof time is determined. In various embodiments, the average rate ofchange of electrolyte concentration within an electrochemical gas sensorover the first period of time may be determined by dividing thedifference between the stored value associated with the electrolyteconcentration of an electrochemical gas sensor at the beginning of thefirst period of time and the electrolyte concentration value measured bythe electrochemical gas sensor at the end of the first period of time(i.e. the value measured at step 701A) by the length of the first periodof time.

Next, at step 705, one or more look-up tables correlating a rate ofchange of electrolyte concentration within an electrochemical gas sensorto a corresponding ambient humidity value at various ambient temperatureand electrolyte water vapor pressure values are generated and storedwithin in a memory module (e.g., memory 504). In various embodiments,each look-up table may define the relationship between a rate of changeof electrolyte concentration within an electrochemical gas sensor to acorresponding humidity value for a given ambient temperature/electrolytewater vapor pressure combination.

Next, at step 706, a stored look-up table to determine the averagehumidity value of the ambient environment over the first period of timebased on the average rate of change of electrolyte concentration withinthe electrochemical gas sensor over the first period of time is used. Invarious embodiments, the appropriate look-up table configuration may begenerated and/or determined based on the measured average ambienttemperature and average electrolyte water vapor pressure over the firsttime period. In various embodiments, the generated look-up table mayindicate that the measured average rate of change of electrolyteconcentration within the electrochemical gas sensor over the firstperiod of time may correspond to a specific ambient humidity value. Invarious embodiments, that specific corresponding ambient humidity valuemay be determined to be the average humidity value of the ambientenvironment over the first period of time.

FIGS. 8-10 each show graphical representations of the data collected invarious experimental trials of embodiments of the claimed invention.FIGS. 8-10 each graphically illustrate the relationship between relativehumidity and the rate of change of electrolyte concentration within anexemplary electrolyte gas sensor. As shown in FIGS. 8-10, the relativehumidity may is measured along the y-axis and the rate of change ofelectrolyte concentration is measured along the x-axis. In variousembodiments, FIGS. 8-10 may graphically illustrate data defined by oneor more exemplary look-up tables as described herein.

The data represented by FIG. 8 represents the behavior of a volume ofacid-based electrolytes in an electrolyte-based electrochemical gassensor over a period of time at a constant 20 degrees Celsius. Theinitial electrolyte concentration was 5 M at the beginning of the periodof time. The illustrated relationship is defined by the equationy=−70.956x+62.694, with an R² value of 0.9999.

The data represented by FIG. 9 represents the behavior of a volume ofacid-based electrolytes in an electrolyte-based electrochemical gassensor over a period of time at a constant 20 degrees Celsius. Theinitial electrolyte concentration was 5 M at the beginning of the periodof time. The illustrated relationship is defined by the equationy=−37.403x+62.968, with an R² value of 0.9996.

The data represented by FIG. 10 represents the behavior of a volume ofacid-based electrolytes in an electrolyte-based electrochemical gassensor over a period of time at a constant 10 degrees Celsius. Theinitial electrolyte concentration was 5 M at the beginning of the periodof time. The illustrated relationship is defined by the equationy=−141.97x+62.536, with an R² value of 1.

As can be understood from the figures and descriptions presented above,the accuracy of the method for determining the average humidity value inan ambient environment by an electrochemical gas sensor may varyproportionally with the ambient temperature. That is, as the temperatureincreases, the accuracy of the determined average humidity improves; asthe temperature decreases, the accuracy of the determined averagehumidity worsens. For example, using an embodiment of the method asdescribed herein, in an ambient environment that is 20 degrees Celsius,the average humidity value over a one-week time period may be measuredto an accuracy of within 7%. Further, in an ambient environment that is30 degrees Celsius, the average humidity value over a one-week timeperiod may be measured to an accuracy of within 14%. Similarly it may beunderstood that the increasing the length of the time period over whichthe measurements described above are taken is understood to improve theaccuracy of the measured average humidity in proportion. In variousembodiments, the an exemplary time interval for measurement may comprisebetween five minutes and one month (e.g., one week).

Conclusion

Many modifications and other embodiments will come to mind to oneskilled in the art to which this disclosure pertains having the benefitof the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that thedisclosure is not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed is:
 1. A gas detection apparatus comprising: afirst electrolyte-based electrochemical gas sensor configured to measurean electrolyte concentration within the first electrochemical gassensor; a temperature sensor configured to measure a temperature of anambient environment surrounding the first electrolyte-basedelectrochemical gas sensor; and a controller configured to determine anaverage humidity value of the ambient environment based on an averageambient temperature and an average rate of change of electrolyteconcentration measured over a period of time.
 2. The apparatus of claim1, wherein the first electrochemical gas sensor comprises a volume ofacid-based electrolyte.
 3. The apparatus of claim 1, wherein thecontroller is further configured to determine an average electrolytewater vapor pressure over a period of time.
 4. The apparatus of claim 1,further comprising a gas detection apparatus housing, wherein the gasdetection apparatus housing comprises an exterior housing portion and aninterior housing portion, and wherein the first electrochemical gassensor, the temperature sensor, and the controller are enclosed withinthe interior housing portion.
 5. The apparatus of claim 1, wherein theaverage humidity value of the ambient environment over the first periodof time is determined using a look-up table correlating the average rateof change of electrolyte concentration within the first electrochemicalgas sensor over the first period of time to a corresponding humidityvalue at the average ambient temperature and an average electrolytewater vapor pressure within the first electrochemical gas sensor overthe first period of time, wherein the corresponding humidity valuedefines the average humidity value of an ambient environment over thefirst period of time.
 6. The apparatus of claim 1, further comprising asecond electrochemical gas sensor, wherein the second electrochemicalgas sensor is an electrolyte-based electrochemical gas sensor positionedwithin the ambient environment, and wherein the first electrochemicalgas sensor is configured to communicate the average humidity value ofthe ambient environment over the first period of time to the secondelectrochemical gas sensor.
 7. The apparatus of claim 6, wherein thesecond electrochemical gas sensor comprises a volume of non-acid-basedelectrolyte.
 8. The apparatus of claim 6, wherein the secondelectrochemical gas sensor is configured to apply an appropriatecompensation factor to an output of the second electrochemical gassensor based on the average humidity value of the ambient environmentover the first period of time.
 9. The apparatus of claim 1, furthercomprising a communication module for communicating calculated averagehumidity value to other devices in IoT network for displaying and/orprocessing the received values.
 10. A method of determining ambienthumidity comprising: measuring electrolyte concentration variation in afirst electrolyte-based electrochemical gas sensor; measuringtemperature of ambient environment surrounding first electrolyte-basedelectrochemical gas sensor using a temperature sensor; determining,using a controller, an average humidity value of the ambient environmentover the first period of time based on an average ambient temperatureand an average rate of change of electrolyte concentration measured overa period of time.
 11. The method of claim 10, wherein the firstelectrochemical gas sensor comprises a volume of acid-based electrolyte.12. The method of claim 10, wherein the controller is further configuredto determine an average electrolyte water vapor pressure over a periodof time.
 13. The method of claim 10, wherein the temperature sensor isintegrated into the first electrochemical gas sensor.
 14. The method ofclaim 13, further comprising providing a gas detection apparatushousing, wherein the gas detection apparatus housing comprises anexterior housing portion and an interior housing portion, and whereinthe first electrochemical gas sensor, the temperature sensor, and thecontroller are enclosed within the interior housing portion.
 15. Themethod of claim 10, wherein the average humidity value of the ambientenvironment over the first period of time is determined using a look-uptable correlating the average rate of change of electrolyteconcentration within the first electrochemical gas sensor over the firstperiod of time to a corresponding humidity value at the average ambienttemperature and an average electrolyte water vapor pressure within thefirst electrochemical gas sensor over the first period of time, whereinthe corresponding humidity value defines the average humidity value ofan ambient environment over the first period of time.
 16. The method ofclaim 10, further comprising providing a second electrochemical gassensor and communicating the average humidity value of the ambientenvironment over the first period of time from the first electrochemicalgas sensor to the second electrochemical gas sensor, wherein the secondelectrochemical gas sensor is an electrolyte-based electrochemical gassensor positioned within the ambient environment.
 17. The method ofclaim 16, wherein the second electrochemical gas sensor comprises avolume of non-acid-based electrolyte.
 18. The method of claim 17,further comprising applying an appropriate compensation factor to anoutput of the second electrochemical gas sensor based on the averagehumidity value of the ambient environment over the first period of time.